Malolactic Fermentation: Why Some Wine Tastes Creamy

Malolactic fermentation is a second conversion that happens after the yeast have finished their work, in which bacteria turn the sharp malic acid in wine into softer lactic acid. The wine ends up less tart and rounder in the mouth. It happens in nearly every red wine and in some whites, Chardonnay most famously of all, and while it can throw off a buttery aroma, it very often doesn't.

That last part is where most explanations of this stop being useful. You've probably read that malolactic fermentation is what makes Chardonnay taste like butter, which is true often enough to be worth saying and wrong often enough to leave you picking bottles on a rule that doesn't hold. Plenty of wines go through it and taste nothing like butter. Plenty of creamy whites never went through it at all. Once you know what's actually going on, the word stops being trivia and starts being something you can use in a shop.

What is malolactic fermentation, in plain English?

It's a bacterial conversion of one acid into another, and it changes how a wine feels rather than what it tastes of. Once the yeast have turned grape sugar into alcohol and gone quiet, a different set of microbes gets going. These are lactic acid bacteria, and the one doing most of the work in wine is a species called Oenococcus oeni.

What they eat is malic acid, which is the hard, green acid you know from biting into an underripe apple. What they leave behind is lactic acid, the gentler one you know from yogurt and milk. Chemically the swap is a decarboxylation, so a little carbon dioxide gets released along the way, which is why a wine in the middle of the process looks cloudy and faintly fizzy sitting in the tank. Wikipedia's entry on malolactic fermentation lays out the chemistry if you want the long version.

The name causes more confusion than anything else about it. We call it a fermentation, but no alcohol gets made and no sugar gets used. Most winemakers just say "malo" and move on. The effect on the finished wine is that total acidity falls, the pH creeps up slightly, and the whole thing reads as softer and fuller across your tongue. If you want the background on why that matters so much, we've written separately about acidity in wine and what it does to everything else in the glass.

Why does malolactic fermentation make wine taste buttery?

Sometimes it does and sometimes it doesn't, and the difference comes down to how long the winemaker waits. The butter smell comes from a single compound called diacetyl, which the bacteria produce as a byproduct rather than as the point of the exercise. On its own, diacetyl smells almost exactly like buttered popcorn, which is why the association is so strong once you've noticed it.

Diacetyl shows up early in the process, and if the bacteria are allowed to carry on working they break it back down into acetoin and 2,3-butanediol, which smell far gentler. The spent yeast sitting in the bottom of the barrel do the same job. Matthew Rorick of Forlorn Hope Wines told SevenFifty Daily that his general rule is to wait two or three weeks after malo finishes before racking the wine or adding sulfur, and cited data he was shown at UC Davis indicating that by twenty days post-malo, diacetyl levels typically fall below the human sensory threshold, assuming no sulfur addition and continued contact with the yeast lees.

So the buttery style is a decision rather than a consequence. A producer who wants it racks the wine off early and locks the compound in place. A producer who doesn't want it waits, and the same process delivers texture without the popcorn note. Two Chardonnays can both have gone through full malo and land in completely different places.

Oak is the other variable people fold into this, and it's genuinely separate. The vessel makes no difference to whether malo happens, and it runs perfectly well in a stainless steel tank. Oak contributes vanilla, toast and baking spice; malo contributes texture. They travel together in a lot of California Chardonnay, so the two get treated as one thing. The South African producer Ken Forrester never allows his Chenin Blanc to go through malo because he wants to keep the acid, and his reserve wines still come out smooth and creamy, purely from barrel aging. If you want the practical version of all this, our guide to spotting a buttery Chardonnay on a wine list works from the words rather than the chemistry.

Why do you taste it in Chardonnay but not in Cabernet?

Because red wine hides it, and it hides it very effectively. The threshold at which a person can detect diacetyl is much higher in red wine than in white, and it's highest in reds carrying a lot of polyphenols, which means grapes like Cabernet Sauvignon. All the tannin and pigment and other material pulled out of the grape skins gives your nose a great deal else to deal with, and the buttery compound gets lost in the crowd. A white wine has almost none of that material, so the same quantity of diacetyl arrives unmistakably.

This is the reason the Chardonnay association stuck so hard, and it's also why the association is backwards. Malolactic fermentation is considerably more common in red wine than it is in Chardonnay. Winemakers almost never stop it in reds, while they routinely block it in whites, and the trade publication SevenFifty Daily makes exactly this point in its survey of what people get wrong about malo. Nearly every red wine you've ever drunk went through it. You just had no way of knowing.

What the process does in red wine is worth knowing anyway, because it isn't nothing. Lower acidity makes tannin feel rounder and less abrasive against your gums, which is a large part of why an approachable red feels approachable. The same article reports studies showing that malo intensifies red berry aromas, particularly in lower pH wines where the fruit can otherwise read as muted, and that it tones down green or vegetal notes at the same time. If tannin is the thing you struggle with in red wine, our piece on what wine tannins actually are covers why softening them changes the experience so much.

Which wines go through malolactic fermentation?

Almost all reds, a good share of fuller whites, and deliberately none of the wines whose whole appeal is their bite. The decision belongs to the winemaker in every case, and it gets made on what the wine is supposed to feel like when someone opens it.

The logic behind blocking it in whites is mostly about climate. Grapes lose malic acid as they ripen, so fruit from a warm region or a hot year arrives with less acid to spare in the first place, and a winemaker who lets malo take another chunk out ends up with a flabby wine. The usual method for stopping it is adding sulfites once the alcoholic fermentation has finished, which keeps the bacteria from ever getting started. Riesling and Gewurztraminer get this treatment as a matter of course, because a Riesling without its acid isn't really a Riesling.

Can you tell from the label or the wine list?

Not by looking for the term itself, which almost never appears on a front label, but the words producers do use will get you most of the way there. What you actually care about is texture, and texture is what those words describe.

A back label or a shelf talker reading barrel-fermented, barrel-aged, creamy, rounded, toasty or sur lie is pointing at the fuller end of the range. That last one means the wine sat on its spent yeast for a while, which builds body in much the same direction. Words like stainless steel, unoaked, crisp, mineral, zesty and bright are pointing the opposite way, toward a wine that kept its edge. None of these terms proves that malo did or didn't happen, and that's fine, because the thing you're trying to predict is how the wine will feel rather than which microbes were involved. Our guide to finding an unoaked Chardonnay goes through the shelf vocabulary in more detail, and if Chardonnay in general is the puzzle, we've covered what Chardonnay actually tastes like across both styles.

At a restaurant, asking whether a wine went through malolactic fermentation is a worse question than it sounds. Your server may not know, the sommelier may not have the technical sheet, and the answer still wouldn't tell you whether you'd enjoy the bottle. Ask for what you want instead. Saying you'd like a white with some weight to it and not much sharpness gets you a useful recommendation in about four seconds, and it works on anyone who knows their list.

The harder version of this problem is standing in a shop holding a bottle whose back label says nothing at all, which happens constantly. That's the moment Fit Check is built for: you point your phone at the bottle or type in the name, and Sommy tells you whether that specific wine lines up with what you already like, rather than describing it in words you'd still have to interpret.

Does it change what food the wine goes with?

Yes, and the mechanism is straightforward once you know malo took acid out of the wine. Acidity is the thing that cuts through fat and salt on your plate, so a wine that went through full malo has less of that cutting power and works better by keeping company with a rich dish than by contrasting against it.

Roast chicken with a pan sauce, lobster with drawn butter, a mushroom risotto, a wedge of soft cheese: a rounder Chardonnay settles alongside all of those without any friction. Turn the plate toward fried food, a squeeze of lemon, a sharp vinaigrette or a dozen oysters, and you want the acid back, which is where a wine that skipped malo does far more work. Our picks for creamy pasta night run through the same logic across Alfredo, carbonara and pesto, which each pull in a slightly different direction.

With red wine the effect is quieter, mostly because you're feeling it as tannin rather than tasting it as acid. A red that's been softened this way handles a gentler dish than its grape variety alone would suggest, so a Cabernet with rounded tannin can sit next to roast vegetables in a way that a fiercer one would bulldoze.

Common questions about malolactic fermentation

Is malolactic fermentation the same as regular fermentation?

No, and they don't even involve the same organisms. Primary fermentation is yeast turning grape sugar into alcohol, which is the one that makes wine wine. Malolactic fermentation is bacteria converting one acid into another acid afterwards, producing no alcohol whatsoever. The shared name is a historical accident more than a description.

Does malolactic fermentation make wine sweeter?

It doesn't add any sugar, so a dry wine that has been through it is still dry. What changes is that removing sharp acid lets the fruit flavors already present come forward more easily, so the wine can read as riper or rounder without a gram of sugar having moved anywhere.

Do all red wines go through malolactic fermentation?

Very nearly all of them do, because winemakers want the smoother tannin and rarely have a reason to prevent it. Exceptions turn up in wines made by carbonic maceration, the technique behind a lot of Beaujolais, because that process eats the malic acid before any bacteria get a chance at it, a point Mathieu Lapierre of Domaine Lapierre in Morgon makes in the same SevenFifty piece.

Can you actually taste malolactic fermentation in a wine?

You can feel it more reliably than you can taste it. The honest answer is that the texture difference is easy to pick up once you've compared two versions of the same grape side by side, while the buttery aroma is only there in a subset of wines and disappears entirely in reds.

Is malolactic fermentation natural or is it added?

Both of those happen in practice. The bacteria live in cellars and on equipment anyway, so the process can start on its own, and for centuries that's exactly what it did: winemakers recorded a mysterious activity in their barrels during the warm spring months after harvest long before anyone knew what was causing it. Modern producers usually inoculate with a selected strain instead, because leaving it to chance invites bacteria that produce genuinely unpleasant results.

Does it lower the alcohol in the wine?

It doesn't change the alcohol at all, in either direction. No sugar gets consumed and none gets created, so a wine comes out of malo at exactly the strength it went in. What shifts is the acid balance and, through that, the way the alcohol reads on your palate, which can make a wine feel slightly warmer and softer than the same number would suggest elsewhere.

Choosing by texture rather than by grape

The reason this is worth the ten minutes is that it moves your buying decision off the grape name and onto something that actually predicts your experience. Chardonnay isn't one thing, and neither is any other variety with a range this wide. The same grape, from the same region, in the same year, gives you a taut and lemony wine or a broad and creamy one depending on choices made in a cellar months before the bottle reached the shelf.

So decide which of those you want before you start reading labels. If you want a wine that soothes a rich plate, look for the barrel and lees vocabulary and accept that you might get a little butter along with it. If you want a wine that cuts and refreshes, look for steel and stone and citrus, and treat the absence of those words as a warning rather than a neutral signal. The chemistry underneath is the same either way, and the only question that matters is which one you'd rather be drinking tonight.